Electromagnetic actuator



United States Patent 3,378,732 I ELECTRQMAGNETIC ACTUATOR Gerald E.Diets, Milwaukee, and Russell E. Matthews, (leonomowoc, Wis, assignorsto Penn @ontrols, lino, Gosheu, End, a corporation of Indiana Filed Apr.15, 1%5, Ser. No. 448,534 14 Claims. (Cl. 317-123) ABSTRAQT 0F THEDlSfiLU SURE A non-impact solenoid in which the path of the plunger isextended beyond the coil end by means of a hollow magnetic cap whichterminates one end of the nonma netic plunger guide. When the coil isenergized, the plunger attains a magnetic null position withoutimpacting the end cap. This null position is attained by balance of themagnetic forces interconnecting the plunger with the end cap and asubstantially large washer of magnetic material positioned encirclingthe open end of the plunger guide.

The invention relates to electromagnetic actuators and especially tothose equipped for energization from an alternating current source.

Electromagnetic actuators adapted for energization from alternatingcurrent sources, in general, comprise an energizing electromagnetic coilmounted encircling a sleeve or tube of non-magnetic material in which aplunger is slidably disposed for guided movement along the coil axis.The plunger is usually biased by a spring toward a normally unactuatedposition. A magnetic circuit path is provided for the flux generated bythe coil by a magnetic frame upon which the coil is mounted. The path issuch as to cause the flux to magnetically couple the plunger, underconditions Where the coil is energized, to actuate the plunger againstits spring bias along the coil axis. The magnetic frame includes a polepiece terminating one end of the guide sleeve of the plunger. The polepiece acts as an end stop which the plunger strikes when it is actuated.To prevent drop-out of the plunger and also chatter of the plungeragainst the pole piece during variations of the flux (due to theinherent cycling of the alternating current source) a shading ring isprovided encircling the depending pole piece within the guide sleeve.This shading ring acts as a shorted turn in which induced current flowcreates suliicient flux to maintain the plunger in its actuated positionagainst the pole piece preventing drop-out and chatter. Such actuators,be cause of the necessity that the plunger strike the pole piece, arenoisy.

In certain applications of electromagnetic actuators it is desirablethat their operation be completely noiseless. In other applications,although some operating noise may be tolerated, what may be termed quietoperation is desirable.

It is, therefore, an object of the invention to provide anelectromagnetic actuator adapted for energization from an alternatingcurrent source, which actuator is readily adaptable to variousapplications, and yet is of simple construction, reliable in operation,and may be economically manufactured and maintained.

It is another object to provide such an electromagnetic actuator whichis noiseless.

It is yet another object to provide such an electroma netic actuatorwhich, while not completely noiseless, is of substantially quietoperation being free of the noise due to impact of the plunger against astop and of hum type noise.

Still another object is to provide such an actuator which 3,378,732Patented Apr. 16, 1968 may be readily and simply assembled anddisassembled into any one of three desired constructions, that is, thecompletely noiseless, the quiet, or the impact type actuator.

The invention involves providing for noiseless operation anelectromagnetic actuator with two rectifiers connected in the circuit ofits energizing coil, one to provide half-wave rectified direct currentfor energizing the coil, and the other connected directly across thecoil to provide a current path which tends to maintain the flux fieldgenerated by the coil during variations of the applied current. Theplunger and magnetic circuit are constructed such that the plunger isactuated to a null position where the net magnetic forces acting upon itbalance the biasing force of its spring to maintain the plunger in suchposition so long as the coil remains energized. The plunger is broughtand maintained in this actuated position without impact against a stop,and maintained there Without noise which may be termed hum. One end ofthe plunger is stepped or necked down slightly to conform to theconfiguration of a magnetic end cap closing one end of the guide sleevein which the plunger is disposed to provide a fixed air gap between theplunger and the magnetic end cap, when the plunger is in its actuatedposition. This fixed air gap prevents the plunger being maintainedactuated after its energizing coil is disconnected from the alternatingcurrent source.

To provide a quiet operating actuator, the fore going described actuatoris modified by omitting the rectifier shunting the coil and substitutingtherefor a relatively large shading ring of copper, encircling the endcap terminating the guide sleeve. The shading ring acts as a shortedturn and is of sufficient mass that currents induced therein by thecollapse of the generated flux field produce sufficient flux during theblocked half-cycle of the applied power to maintain the'plungermagnetically coupled in its null position and minimizing A.C. hum. Thisconstruction requires no impact of the plunger against a stop andmaintains the plunger in an actuated position by balancing the magneticforces acting on the plunger against the force of the biasing spring.

To provide the impact type actuator, the first described actuator ismodified by removing both rectifiers from the coil circuit and byproviding a pole piece and encircling shading ring of copper Within theguide sleeve at the capped end, against which pole piece the plungerstrikes and is maintained by the shading ring.

Features and advantages of the invention may be seen from the above,from the following descriptions of the preferred embodiments whenconsidered in conjunction with the drawing in which, like numeraldesignations refer to like parts in different figures, and from theappended claims.

In the preferred embodiment, the electromagnetic actuator will be shownas operating a valve for controlling the flow of a fluid through aportal, it being understood nevertheless, that the invention is not solimited, and the actuator may be used in other similar arrangementsrequiring solenoid type actuation.

In the drawing:

FIGURE 1 is a simplified diagrammatic cross-sectional view, in frontelevation, of an electromagnetically actuated valve, embodying theinvention and showing the electromagnetic actuator assembled fornoiseless operation;

FlGURE 2 is a top view on a smaller scale of the electromagneticallyactuated valve of FIG. 1;

FIGURE 3 is a simplified schematic diagram of the electrical circuit ofthe electromagnetic actuator of FIG. 1;

FIGURE 4 is a fragmentary, cross-sectional view of the upper portion ofan electromagnetic actuator similar to that of FIG. 1 but modified forquiet operation; and

asravsz FIGURE 5 is a fragmentary, cross-sectional view similar to thatof FIG. 4, showing the electromagnetic actuator of FIG. 1 modified foroperation as an impact ty e.

Referring to FIGS. 1, 2, and 3, in general, the electromagnetic actuatorof the valve comprises an cnergi ing coil assembly, generally designated12, a cylindrical plunger 14 of magnetic material slidably disposed forlongitudinal movement in a guide tube 16 of non-magnetic material, and amagnetic frame assembly, generally designated 18, housing coil assembly12 and tube 16.

The lower end of plunger 1d is provided with a necked down portion 29 towhich the upper portion of a valve head 22 is attached by means of pin24 extending through pin recei apertures coaxiali aligned in plungerportion and valve head 22. Pin 24 is held in place by a retainer ring 26disposed in peripheral groove formed in valve head 22.

Valve head 22. is provided at its lower end with a cir cular disc-likeportion 30. A resilient valve member 32, such as rubber, is bonded tothe bottom surface of valve head portion 39 for seating engagement withan annular seat 36 interconnecting inlet fluid passageway 33 to outletpassageway l-tl defined in valve body 42. to control fiuid fiowtherethrough.

A conical compression spring 46 encircles the lower portion of plunger14 with one end against the upper surface of valve head 22 and with itsother end under compression against the inside surface 56' of aninverted cup-like portion 52 of magnetic frame assembly 18. Spring 46biases plunger 14 in the position shown in solid outline in FIG. 1,biasing valve head portion 32 against valve seat 36 closing the portalbetween fluid passageways 3S and 4t}.

Coil assembly 12 includes a coil 6%) wound on a spool 62 and tworectifiers 64, d6 interconnected in the coil energizing circuit as shownin FIG. 3. Coil may be energized from any suitable alternating currentsource over input leads 68, 7d of the coil circuit. Rectifier 64 isconnected between input lead as and one end of coil 60 to providehalf-wave rectification of the applied alternating current voltage. Thesecond rectifier 66 directly shunts coil as with its cathode connectedto the junction of the cathode of rectifier 4 with the end of coil 6%.Rectifier 66 tends to oppose the decay of the fiux field of coil 60,under conditions where the coil is ole-energized on the alternatehalf-cycles of the applied current which are blocked by rectifier 64.Rectifiers 64 and 6d are taped onto spool 62 (FIG. 1) with coil 60;input leads 68, '70 passing through an eyelet '74 provided in frameassembly 18 for connection to an energizing source.

Inverted cup portion 52 of magnetic frame assembly 18 supports acircular washer 78 of magnetic material which is attached thereto, asfor example, by means of welding. Guide tube 16 extends through alignedholes defined centrally in member 51?. and washer 73, and is provided atits bottom with a turned out rim 16a nesting within cup member 52 andattached thereto. A cap of magnetic material is secured to the upper endof non-magnetic tube to by any convenient manner such as by brazin". Cap8% is bored out, extending the guide tube for plunger 14 beyond theupper end of coil spool 62 and terminating it.

A cover 82 of magnetic material and hollow cylindrical shape closed atthe upper end forms part of magnetic frame assembly 18. Cover 82 is ofrelatively thin walled construction and has defined in its top wall acentrally located hole through which a portion Sila of cap St)protrudes, when the cover is placed over coil assembly 12. The bottom ofcover 32 is formed into an outwardly extending flange 52a which restsover a similar flange 52a of cup member 52. The upper portion title ofcap 80 is provided with external threads for cooperation with a nut 84to secure cover 32 in place. Cap 8%, cover 252, cup member 52, andWasher '78 together comprise magnetic field assembly 18 ofelectromagnetic actuator 4 10, providing a predetermined magneticcircuit path for the flux field generated by current fiow through coil6%.

With actuator it? assembled and valve head 22 attached to plunger 14, asshown in FIG. 1, actuator ltl is bolted to valve body 42 by means offasteners threaded into the vznve body; fasteners 93 extending throughaligned holes in flanges 5.2a and 82a. Spring 45 biases valve head 22.into seating engagement with seat 35, preventing fiuid flow through theValve.

It may be noted that the lower inner surface of cap 8t? is reamed outfor a short distance at 8d to receive the upper end of non-magnetic tube16 and provides a smooth tubular guide surface for plunger 14 into cap853 at the junction of the tube and cap. Plunger 14 is of lengthcalculated to extend only a certain distance into magnetic cap 89 underconditions where coil 69 is energized. This actuated position of plunger14 is indicated by he broken-line outline in FIG. 1 of the upper portion14a of plunger 14 and a part of valve head 22 shown lifted off of valveseat 315. The bottom of plunger 3.4 in such actuated condition is raisedto substantially the level of washer 73. The upper portion Ma of plunger14 is necked down or stepped to provide a fixed air gap radially betweenplunser 14 and cap bit. This prevents the occurrence of suflicientresidual magnetic attraction between plunger 1 cap 8t) as to interfereappreciably with the return of the plunger to unactuated condition,after coil 59 is dc-energized, thereby avoiding what may be termedmagnetic hang-up of the plunger.

If desired, a portion of plunger 14 may be necked down (not shown)intermediate its ends to minimize its Weight. However, the two endportions of plunger 14 must closely follow the interior wall surface ofthe "aide tube for proper guiding and magnetic coupling of the plunger.

Assume that coil 60 is energized through rectifier 64 from analternating current source connected to leads 6%, 7h. The fiux fieldgenerated by current flow through coil 60 each unblocked halfcycle ofthe applied current is channeled by magnetic frame assembly 18 tomagnetically couple plunger 14, actuating it towards its open valveposition, shown in bYOliCR-li1i outline in FIG. 1. This lifts valve head22 off seat 35, permitting fluid flow between inlet and outletpassageways 38, 46. Magnetic fiux flows through the magnetic pathprovided by washer 78, cup member 52, cylindrical cover 82, cap 89,across the air gap between cap fill and the upper end of plunger 14,through plunger 14, and from the bottom end of the plunger across theair gap to washer 78. This magnetic coupling urges plunger 14 upward toa position where the net resultant of the magnetic forces urging plunger14 upward are balanced by the forces of spring 46 biasing the plungerdownward. Plunger 14 domes to a stop at some distance from the closedend of cap 39, as shown in rolren-line outline. This balanced positionis due to the selection of the plunger length in relation to theposition of cap 89 and washer '73. The length is such that the magneticforces coupling the bottom and top portions of plunger 14- to themagnetic frame assembly 18 are substantially balanced when plunger 14spans the distance between cap 39 and washer 78; spring 46 beingselected with a spring force merely sufllcient to return plunger 14 tounactuated position. Plunger 14 is, thus, magnetically balanced inactuated position at some distance from the closed end of its guidetube. This prevents plunger 1 from striking the closed end cap 89,providing actuation of valve 22 without impact noise.

Rectifier 66 opposes decay of the flux field of coil 64 during blockedhalf-cycles of the applied current by providing a current path shuntingthe coil for current induced in coil 6% by its collapsing flux field.The magnetic forces coupling plunger 6% are, thus, maintainedsufliciently during blocked half-cycles to maintain plunger 14 inactuated position and to effectively eliminate noise due to AC. hum.

As was previously stated, the upper end 14a of plunger 14 is stepped ornecked down to provide a fixed air gap between end cap 80 and theplunger end. This fixed air gap prevents magnetic hang-up of plunger 14,when coil 60 is disconnected from its energizing alternating currentsource.

For applications where some noise may be tolerated but quiet operationis desired, the electromagnetic actuator and valve of FIG. 1 may bemodified, as shown in FIG. 4 and as follows: The shunting rectifier 66is omitted from coil assembly 12, only rectifier 64 being provided inthe coil circuit. With only this modification, it was discoveredexperimentally that although plunger 14 is actuated in guide tube 16toward a magnetically balanced or null position without impact againstthe closed end of cap 30, variations inherent in the half-wave rectifiedcurrent fed to coil 60 by rectifier 64 tended tooscillate the plunger,producing objectionable A.C. noise or hum. A washer or shading ring 92of electrically conductive material, such as copper, and of relativelysubstantial mass relative to the size of plunger 14 and coil 60 wasprovided on top of coil 60 encircling cap 80. Copper washer 92 selectedin one tested embodiment of a diameter substantially twice that ofplunger 14 and of a thickness approximately one-half the radius ofplunger 14-. Washer 92 need not be circular but may be rectangular. Allthat is required is that it act as a shorted turn providing a shortedcurrent path in which enough current flow is induced by the collapsingof the flux field of coil 60 during blocked halfcycles of the appliedcurrent to provide suficient flux magnetically coupling the upper end14a of plunger 14 to cap 89 to maintain plunger 14 in its actuatedposition and minimize A.C. hum.

If desired, a plunger biasing spring 94 may be disposed in the upper endof the guide tube formed by non-magnetic tube 16 and cap 80, and theconical spring 46, shown in the embodiment of FIG. 1, discarded.

In operation the modified arrangement of FIG. 4 operates similar to thatdescribed for the embodiment of FIG. 1; rectifier 64 again acting torectify the applied alternating current to half-wave direct current.Under such conditions, shading ring or washer 92 functions as a shortedturn providing sufficient flux during blocked half-cycles of the appliedpower to maintain plunger 14 in its actuated position againstoscillation, thereby eliminating the objectionable hum. This providesquiet operation of electromagnetic actuator For modification of theelectromagnetic actuator 10 of FIG. 1 to operation which is neithernoiseless nor quiet, a pole assembly 96 (FIG. 5) may be pressed into theinside of cap 89 and both rectifiers 64 and 66 omitted from the coilassembly. Assembly 96 comprises a pole piece 98 of magnetic materialdimensioned to engage the upper end surface of plunger 14 when theplunger is actuated to its uppermost position shown in broken-lineoutline. Encircling pole piece 98 is a small shading ring 166-,preferably of copper, in the form of a copper washer. Ring 1% functionsas a shorted turn to provide suificient flux during fluctuations of themagnetic flux field of coil 60 to maintain plunger 14 in its fullyactuated position against the end surface of depending pole piece 98.Ring 10%) and pole piece 98 are press-fit into an annular retainer 102,which in turn is press-fit into cap 80. In this embodiment the upperportion of plunger 14 is preferably of spherical shape. Thisconstruction provides a conventional electromagnetic actuator in whichcoil 60 is energized directly from an alternating current source,causing actuation of plunger 14 upward against pole piece 98 with impactnoise.

In summary, it can be seen that the subject electromagnetic actuatorscan be readily and economically manufactured from interchangeable partswhich provide for ease of assembly and disassembly of actuators forvarious applications, requiring either noiseless actuators, quiet ones,or where noise is not a factor.

As changes can be made in the above described construction and manyapparently different embodiments of this invention can be made withoutdeparting from the scope thereof, it is intended that all mattercontained in the above description or shown on the accompanying drawingbe interpreted as illustrated only and not in a limiting sense.

What is claimed:

1. An electromagnetic actuator energizable from an alternating currentsource, comprising a plunger of magnetic material, a hollow tube ofnon-magnetic material for slidably receiving said plunger and guidingits movement along the longitudinal axis of said tube, an energizingcoil encircling said tube, and a magnetic frame assembly providing apredetermined magnetic path for flux generated by said coil, saidassembly including a first member of magnetic material substantiallycircumventing said tube adjacent one end thereof, a cap of magneticmaterial closing the other end of said tube, said cap being of hollowcylindrical shape open at one end to extend the tubular guide for saidplunger a predetermined distance beyond the adjacent end of said coil,and a second member of magnetic material interconnecting saidcircumventing member and said cap member to provide a magnetic flux pathfrom said one tube end to said other, the magnetic circuit of which iscompleted across air gaps at said tube ends to said plunger in saidtubular guide causing actuation of said plunger to a c/ertain positionunder conditions where said coil is energized, said plunger being ofsuch longitudinal dimensions with respect to the longitudinal dimensionof said tubular guide such that said plunger when in said certainactuated position extends at least a certain minimum distance beyondsaid adjacent end of said coil into said cylindrical cap.

2. An actuator as set forth in claim 1 wherein there is provided aspring biasing said plunger against actuation by said energizing coil,said spring exerting a force determined to balance the resultantmagnetic force exerted on said plunger by said coil when in saidactuated position.

3. An actuator as set forth in claim 2 wherein a pole piece protrudesinto said tubular guide from said closed end of said cylindrical capplacing its pole face in position for engagement with the adjacent endface of said plunger when the latter is in its said actuated position,and wherein a shading ring of electrically conductive material encirclessaid pole piece within said tubular guide for providing sufiicientmagnetic flux to maintain said plunger actuated during fluctuations ofthe coil generated field in response to normal cyclical changes of theapplied alternating current energizing source.

4. The actuator as set forth in claim 3 wherein said shading ring is inthe form of a washer of copper material.

5. The actuator of claim 3 wherein said pole piece and shading ring areconstructed for insertion in said cap and retention therein throughfrictional engagement with adjacent surfaces.

6. An actuator as set forth in claim 2 wherein said second member ofsaid magnetic frame assembly is in the form of a relatively thin Walledhousing fitting over said coil and tubular guide and is provided with astud receiving aperture formed coaxially with said cap, and wherein saidcap is provided with fastener portion extending through said aperturefor removably securing said second member to said tubular guide.

7. The actuator of claim 2 wherein rectifying means are provided at theinput of said energizing coil for converting the applied alternatingcurrent to half-wave rectified current.

8. An actuator as set forth in claim 7 wherein there is provided ashading ring in the form of a washer encircling said cap and contiguousthereto.

9. The actuator as set forth in claim 8 wherein said washer is of adiameter substantially twice that of said plunger.

10. The actuator of claim 9 wherein said washer is of a thickness atleast one-half the radius of said plunger.

121. The actuator of claim 10 wherein said Washer is of copper material.

12. The actuator of claim 7 wherein there is provided a shorted turn ofelectrically conductive material encircling said cap and dimensionedtoprovide an induced current flow in response to collapsing of the coilgenerated field during blocked half-cycles of the energizing current,which current flow is of a magnitude and duration to provide at leastsufilcient magnetic coupling of said plunger end cap to eliminateeffectively A.C. noise and maintain 10 the plunger in actuated position.

13. The actuator set forth in claim 2 wherein said biasing spring is acoil type spring disposed in said tubular guide between said closed endof said cap and said plunger.

14. The actuator set forth in claim 7 wherein there is provided arectifier directly shunting said coil providing a path for currentgenerated in said coil by collapsing of said coil flux field duringblocked alternate half-cycles of the applied current source, whichcycles are blocked by said half-Wave rectifying means.

References Cited UNITED STATES PATENTS 2,410,320 10/1946 Nasserlein335-245 2,735,047 2/1956 Garner et al 335-251 X 2,856,569 10/1958 Birge335-251 X 3,030,523 4/1962 Pittman 30788.5 3,251,281 9/1964 Kuehn 3171303,215,902 9/1965 Foley et al 335255 X MILTON O. HIRSHFIELD, PrimaryExaminer.

I. A. SILVERMAN, Assistant Examiner.

